Among various glycated proteins, glycated hemoglobin (glycated Hb) in blood serves as an important indicator in the diagnosis, treatment, etc. of diabetes, because it reflects the patient's past history of blood glucose levels.
Measurement of such glycated Hb has been carried out, for example, by high performance liquid chromatography (HPLC), a minicolumn method, an immunoassay, a dye method, or the like. According to these methods, the ratio of glycated Hb to total Hb or the amount of glycated Hb can be determined. However, the above-described HPLC has a problem in that, for example, it requires a dedicated apparatus for measuring glycated Hb, and the immunoassay and the dye method have problems in that, for example, cells used for measurement might be contaminated and the measurement sensitivity might not be sufficient.
On this account, measurement of a glycated protein such as glycated Hb using a redox reaction caused by an enzyme has been utilized in applications such as biochemical analyses and clinical tests, because it can be carried out easily without using a special measuring apparatus.
Such measurement of glycated Hb using a redox reaction is carried out, for example, in the following manner. First, a sample containing glycated Hb is treated with a fructosyl amino acid oxidase (hereinafter referred to as “FAOD”) so that the FAOD acts on a glycation site of the glycated Hb, thereby causing hydrogen peroxide to be formed. The amount of the hydrogen peroxide corresponds to the amount of the glycated Hb. Subsequently, to the sample treated with the FAOD, a peroxidase (hereinafter referred to as “POD”) and a reducing agent are added so that a redox reaction occurs between the hydrogen peroxide and the reducing agent with the POD as a catalyst. At this time, when a reducing agent that develops color when it is oxidized is used, the amount of the hydrogen peroxide can be determined by measuring the color developed. As a result, the amount of the glycated Hb in the sample can be determined.